Akbuk, for years we kept an apartment in Spain, but tired of it. The trip almost always included an overnight (sometimes 2 nights) ferry to Bilbao or Santander. I didn't like it and the long drive down to the south I eventually found too tiring and maintenance was always an issue, so we sold up. My wife had long wanted to try a cruise, but I didn't fancy it, but finally agreed just before we sold up in Spain. The cruise went from Barcelona for 7 days down to the Canaries & back. It meant a short flight from Bristol. We were met, whisked off on a coach to the ferry port. Very little in the way of security was required and we were on board. We had a spacious balcony cabin and it included our first visit of many to Madeira, now possibly my favourite place in the world. Food was great as was the company, in short we had a lovely time and in 7 years have been on 19 cruises around the Atlantic, the Pacific, the Mediterranean, the Baltic and Scandinavia, but have been on none since January 2019. I wouldn't say all have been terrific, but few were regretted. We are tentatively looking at a cruise for September 2021, but will have to wait and see how the winter goes.
As far as sea sickness is concerned, fortunately we both have our sea legs after some very stormy ferry crossings of Biscay. Cruise ships vary in size and therefore stability. Few, except the smallest rock and roll too much and some of the most modern are over 1000ft long so are very stable. The sea however is unpredictable; we have been in the Queen Mary 2 across the Atlantic through the tail of a hurricane with waves breaking over the 8th deck and although not a smooth trip, most people seemed to find the motion acceptable. Other times mid-Atlantic has been like a mill pond, sitting out in the Sun on our balcony.
It might be worth taking a short trip (5-7days) first to see how you go, I would suggest the Med or the Baltic as being generally the calmest. As far as cost, you should remember to factor in parking or getting to either the airport or the cruise port, gratuities (can usually be stopped, although some lines like P&O and Marella, do not charge gratuities) and any guided trips you may wish to take. Drinks packages are expensive, we usually just buy our own as we go as they are about what you would pay in a pub. Excellent meals and snacks are always included in the price, but specialist dining is available as an extra.
I don't think I dare make this longer, but if you need to know any more just ask.
My personal favourite is Marella (Ex Tui) but they rarely depart the UK so flights are required.
Mike.X